1. Field of the Invention
The present invention relates to a numerical control device for controlling a machine tool, and more particularly, to a numerical control device with a servo-output delay unit.
2. Description of the Related Art
In manually feeding axes in, for example, initial setup of a machine tool controlled by a numerical control device, an operator rotates a rotary dial of a manual pulse generator to generate pulses relating to the amount of movement by the manual feed.
Pulse data generated by the manual pulse generator is received by the numerical control device through network communication. The pulse data received by the numerical control device is written to a buffer of the control device. In the numerical control device, the pulse data written to the buffer is read and output to a servo processing unit, thereby driving a servomotor for activating a mechanism section of the machine tool or an industrial machine.
If a communication error occurs in the control device, the pulse data generated by the manual pulse generator is not received by the control device through the network communication. Therefore, the pulse data cannot be written to the buffer in the numerical control device, and a pulse for the cycle concerned is not output to a servo control unit for controlling the servomotor. Consequently, the machine suddenly stops, thereby causing a mechanical shock (see FIG. 8). As shown in FIG. 8, the occurrence of the communication error produces a blank cycle in the pulse data transmitted from the manual pulse generator. Since the pulse data received by the numerical control device becomes discontinuous, drive control of the servomotor for driving the machine cannot be normally performed and a mechanical shock occurs.
For example, claim 2 of Japanese Patent Application Laid-Open No. 2002-268751 discloses a servo control device configured to perform a movement of an axis toward a position intermediate between target positions stored before and after the occurrence of a communication error, if any, during the movement. The servo control device disclosed in this patent document cannot achieve the axis movement precisely corresponding to pulse data output from a manual pulse generator. Thus, according to this conventional method, a previously registered recovery operation is inserted in case of a communication error, so that commanded operations may fail to be achieved.